Underwater electrical cables and marine conductors in general cause major problems when they begin to leak. In some instances leakage is common due to the fact that such cables, and their connectors, commonly operate in subsurface environments, or in near surface atmospheric environments characterized by extreme salt and humidity, wave action, tugging and bending due to ships, boats or other vehicles and exposure to varying weather and environments. The primary sealing means in underwater connectors is generally the insulation encapsulating the strands of individual conductors, or it is an encapsulating material, such as plastic, around the housing of the connector constructed of stainless steel, plastic, high tech plastic or any alloy used for the connector. Frequently, these connectors are made of corrosion resistant metals, such as stainless steel, or the like, and are coated with a plastic or other resistant coating for the purpose of precluding entry of moisture.
Further, in marine seismic operations, underwater electrical plugs or connectors are needed to connect power and instrumentation conductors to other equipment, such as seismic sound generators, i.e. air guns. These “guns” are used as a sound source to obtain acoustic reflections from the sea-floor. Typically, they are fired every ten to fifteen seconds producing extremely strong pressure waves. As a result, the electrical, cables, conductors, and connectors are subjected to a great deal of structural abuse, and normally do not last for extended periods of time before developing leaks or other operational defects. Typically, these components, such as electrical connectors, are exposed to such blasting forces and also to the extremely adverse nature of the environment and will not last long if they are not able to withstand environmental and operational conditions. Therefore, all of the electrical connectors and other components used in these harshest of environments must necessarily withstand repeated explosive forces on their exteriors while allowing for a degree of flexibility within lest the internal conductor be jolted loose from its external housing.
Underwater electrical cables are also subject to movement due to currents, wave action, and the general movement of their fluid environment, which can cause the electrical cables to move in any variety of directions and to be tugged and yanked by the motion of the water. Underwater equipment is frequently connected to instruments on the surface, often to floating rigs on the surface of the water. The motion of the floating rig in relation to the underwater equipment produces great stress on the underwater electrical cable particularly at the cable connection to the underwater equipment. In particular, the connectors endure severe tugging and bending due to movement of the vessel or ship and due to the energy emitted by the guns.
Generally underwater marine connectors are provided with a reinforced tail, which is a sheath of reinforcement around the cable insulation from the electrical connection to some point along the insulated electrical conducting cable to prevent excessive bending at the point where the rigid connector and the conductor are connected. This connector tail of reinforced insulating material protects the electrical cable from excessive bending, at the point where the conductor connects to the connector portion, which might crack the insulating material, exposing the electrical conductor to the water and creating a short of the electrical current. Electrical cables are particularly susceptible to such excessive bending near the point of connection between the electrical cable and the underwater equipment because the equipment fixes the one end of the cable in place, allowing no mobility of the cable to relieve bending stresses on the cable.
Prior tails suffer from a bending focal point at the junction of the tail and the main conductor cable. This is because the prior tails form a substantially rigid and extended reinforced section at the connection between the connector and the cable, thereby moving the bending point from the connection at the connector and cable to the end of the reinforced tail and the more limber and flexible cable. In such an instance, the tail itself, rather than protecting the cable from leakage, can become a source of resistance on the cable and increase the chances that the cable will split and leak at the focal point.
Some of the issues with the prior art have been addressed by U.S. Pat. No. 5,984,714 entitled ELECTRICAL CONNECTOR TAIL, issued Nov. 16, 1999 (Gerrans I), and U.S. Pat. No. 5,885,108, entitled ELECTRICAL CONNECTOR, issued Mar. 23, 1999 (Gerrans both of which are incorporated by reference herein in their entirety. In the Gerrans patents, the bending focal point is moved from the end or terminus of the tail, where the tail and cable meet to a point on the tail itself where the tail provides additional strength to the insulated conductors. This movement of the bending point is achieved by providing a reduced cross-sectional portion or neck portion in the tail. Because this neck portion is close to the connector end and conductor connection the bending occurs at the neck of the tail as opposed to at the terminus of the tail where the insulated conductor provides little strength.
The problem of conductor cable leakage or breakage of the conductor at the junction of the cable and the connector tail is not limited to underwater or marine environments, but is also a problem in any situation where excessive bending of an electrical conductor threatens to compromise the integrity of the electrical circuit.
The problem has been exacerbated by the industry trend towards larger and more powerful air guns. As air guns get larger and more powerful, the forces experienced by the source connector increase and the life of the source connector decreases. Known source connectors experience failures after 15,000 to 25,000 shots of the air gun. Failure after 15,000 to 25,000 shots equates to 1.7 to 2.8 days of continuous service. This service life requires frequent repair or replacement of source connectors that results in unwanted downtime. The short service life also requires that the source connectors be replaced in a reactionary manner, replacing the source connectors only after a failure has been detected.
Thus, what is needed is a source connector with an increase in service life even when used with larger and more powerful air guns.